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The sign accompanying the linear aerospike engine. It reads

The Linear Aerospike Engine

Marshall's Legacy of Flight

Seeking to develop lighter, more powerful launch vehicles capable of versatile
work in Earth orbit, NASA and Lockheed Martin Aeronautics of California
experimented in the late 1990s with an engine without a nozzle. Developed to
support the X-33 Advanced Technology Demonstrator Program here, the linear
aerospike is shaped like an inverted bell turned inside out, "unwrapped" and
laid flat. A series of small combustion chambers along the unwrapped bell
shoot hot gases along its outer surface, producing thrust. The single-stage
X-33 would have been powered by a pair of these engines. Though the X-33
program ended in 2000, the successful development of the linear aerospike
engine is helping engineers refine new ideas for tomorrow's next-generation
propulsion systems.

Linear Aerospike Quick Facts

Propellants:

Liquid Oxygen/Liquid Hydrogen

Thrust (at sea Level):

204,420 lbs.

Height:

7.5 feet

Width:

7.5 feet

Depth:

11.17 feet

While this particular incarnation of the linear aerospike engine was developed
in the 1990s, the aerospike concept dates back much farther.

Rocketdyne had developed a round (referred to as "annular" or "toroidal")
aerospike engine in the late 1960s and planned to submit the engine in the
competition for the Space Shuttle Main Engine. In October 1969 and again in
July 1970 NASA issued statements indicating that they expected the engine to be
chosen for the SSME program to be a "bell-type engine" with a staged combustion
cycle, so Rocketdyne abandoned this effort.

Before development ceased, however, Rocketdyne conducted a test program between
March 1966 and October 1967. Information about this test program is contained
in

Photos of Rocketdyne's annular aerospike engine undergoing a hot-fire is
available from Alternate
Wars; do a search for "NASA/USAF Advanced Development Program (ADP)
Aerospike Engine" and scroll down to the bottom of that section.

Although no longer pursued for the SSME, Rocketdyne did continue its
development on the aerospike concept, producing and test-firing two linear
aerospike engines in the early 1970s. Called the "Linear Test Bed" engines,
the program started in April 1970 when MSFC's Saturn System Office authorized
the work. Research using Linear Test Bed No. 1 concluded in May or June 1972
(depending upon the source), after 44 successful tests; the Linear Test Bed No. 2 work concluded in
October 1973 after 29 successful tests. Never intended for flight, the engines
were constructed of heavy, inexpensive materials and used turbopumps from the
1960s-era J-2S program.

Many of the photos and videos available online showing the hot-firing of a
linear aerospike engine are of the Linear Test Bed engines (including some
photos purported to be of the XRS-2200), which has a wider base than the
XRS-2200. Oddly enough, even a Rocketdyne fact sheet on the RS-2200 includes a
photo of a Linear Test Bed Engine hot-fire test.